Method for preparing laminated article of metallic, polymeric and wax impregnated cellulosic layers

ABSTRACT

A tri-layer laminated article, having an outer wax impregnated cellulosic layer, a middle thermoplastic polymeric layer and an outer metallic layer, is easily prepared by applying a dispersion of solid polymer particles in molten wax to the surface of at least one of the outer layers and then placing the other outer layer adjacent to the dispersion. The application of heat and pressure to the resulting composite causes the cellulosic layer to be impregnated with wax and the polymer to form a molten middle layer. The latter upon cooling, solidifies resulting in the metallic layer firmly adhering to the solid polymeric layer which is firmly adhering to the wax impregnated cellulosic layer. The polymer used must be substantially insoluble in the molten wax at a temperature below the melting point of the polymer and have an adhesive capacity for both metallic and cellulosic materials. The resulting article has utility as a packaging material.

United States Patent 1191 Black et al.

[451 Feb. 13,1973

[ METHOD FOR PREPARING LAMINATED ARTICLE OF METALLIC, POLYMERIC AND WAXIMPREGNATED CELLULOSIC LAYERS [75] Inventors: Ernest P. Black; Irl N.Duling, both of West Chester; John C. Merges, Jr., Glen Mills; Alfred F.Talbot,

Wallingford, all of Pa. [73] Assignee: Sun OiI Company, Philadelphia,Pa.

[22] Filed: Aug. 6, 1970 21 Appl. No.2 61,718

521 US. Cl. ..lS6/309, 156/61, 156/285, 156/313, 161/214, 161/220,161/229,

[58] Field of Search ..l56/6l, 228, 235, 285, 307, 156/309, 311, 313,326; 106/3825, 230, 231; 264/45-48, 111, 261; 161/214, 220, 223, 228,229, 234, 235

Anderson et al. ..16 l/223 X Knepp ..l6l/220 X [5 7 ABSTRACT A tri-layerlaminated article, having an outer wax impregnated cellulosic layer, amiddle thermoplastic polymeric layer and an outer metallic layer, iseasily prepared by applying a dispersion of solid polymer particles inmolten wax to the surface of at least one of the outer layers and thenplacing the other outer layer adjacent to the dispersion. Theapplication of heat and pressure to the resulting composite causes thecellulosic layer to be impregnated with wax and the polymer to form amolten middle layer. The latter upon cooling, solidifies resulting inthe metallic layer firmly adhering to the solid polymeric layer which isfirmly adhering to the wax impregnated cellulosic layer. The polymerused must be substantially insoluble in the molten wax at a temperaturebelow the melting point of the polymer and have an adhesive capacity forboth metallic and cellulosic materials. The resulting article hasutility as a packaging material.

9 Claims, 2 Drawing Figures PATENTED 35173 3. 7 1 6.441

FIGURE l FIGURE 2 Ila .\\\\\\\\\\\\\\\\\\\\\\\Y Hb VIII/MW J l SECTION"A-A" INVENTORS ERNEST P. BLACK 1 IRL N. DULING JOHN C. MERGES JR.ALFREQPF TALBOT BY HUNG-Man ATTORNEY METHOD FOR PREPARING LAlVIINATEDARTICLE OF NIETALLIC, POLYMERlC AND WAX IMPREGNATED CELLULOSIC LAYERSCROSS REFERENCES TO RELATED APPLICATIONS The present application iscopending with the following application filed same date herewith: Ser.No.

61 ,719, I. N. Duling and J. C. Merges, Jr., Method for 1969, by I. N.Duling and J. C. Merges, .lr., which describes a method for preparing apolymer coated, wax impregnated cellulosic substrate. All theseapplications are of common ownership.

BACKGROUND OF THE INVENTION The present invention provides a method forpreparing a tri-layer laminated article having an outer wax impregnatedcellulosic layer, a middle thermoplastic polymeric layer and anotherouter metallic layer. The polymeric layer contributes to the barrierproperties of the finished article and acts as an adhesive. Thislaminated article has utility as a packing material.

Existing methods for preparing laminated articles required severaldistinct processing steps and, therefore, these methods are timeconsuming. One example of such a method is as follows. A cellulosiclayer is dipped in a bath of molten wax and allowed to remain until thewax impregnates the cellulosic layer. Then the wax impregnated layer isremoved from the bath of molten wax and allowed to cool therebysolidifying the wax. Thereafter a suitable thermoplastic polymer isextruded as a molten coating onto the wax impregnated cellulosic layer.The polymer coating is allowed to cool. The resulting product is abi-layer laminated article having a polymeric layer and a waximpregnated cellulosic layer. Afterwards a metallic layer is broughtinto contact with the polymer coating which now has to be heated againto melt the polymer. The subsequent application of pressure and a finalcooling results in a trilayer laminated article.

The present invention provides a simplified method for obtaining thesametri-layer laminated article.

' SUMMARY OF THE INVENTION A tri-layer laminated article can be easilyprepared by this invention, said articlehaving an outer metallic layerand a middle thermoplastic polymeric layer and an outer wax impregnatedcellulosic layer. In this invention a dispersion of solid polymerparticles in molten wax, maintained at a temperature below the meltingpoint of the polymer, is applied as a coating to a surface of either themetallic layer or porous cellulosic layer. The other layer, i.e.,'thelayer to which the dispersion is not applied, is brought into contactwith the dispersion and heat and pressure are applied. Alternatively,the dispersion can be'applied to both outer layers either simultaneouslyor at different intervals and then the dispersion coated surfacesbrought into contact with each other before heat and pressure areapplied. In either alternative substantially all the molten wax isabsorbed by the cellulosic'layer and the heat causes the polymerparticles to melt and the pressure causes the melted particles to form amiddle molten layer. Upon cooling, the molten polymer solidifies and thetri-layer laminated article is formed.

The thermoplastic polymer, used in the aforementioned invention, is onethat is substantially insoluble in molten wax at a temperature below thepolymers melting point and has an adhesive capacity for both cellulosicand metallic materials.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 schematically illustrates onemethod of forming the tri-layer laminated article in accordance with theinvention.

FIG. 2 is a cross-sectional view of the finished laminated product.

DESCRIPTION One method of preparing the tri-layer laminated articleaccording to this invention is illustrated in FIG. I. Thermoplasticpolymer particles and solid wax are placed in a suitable container 1.The temperature of the polymer and wax in the container is raised toabove the melting point of the wax but below the melting point of thepolymer by a suitable heater 2. The temperature of the dispersion ismaintained within this throughout the application step. After the waxmelts, sufficient agitation is applied by a conventional mixer 3 to keepthe finely divided polymer uniformly distributed throughout the moltenwax. The dispersion 4 in the container 1 is transferred, in thisillustration, by gravity to between the two outer layers, the cellulosiclayer 5 and the metallic layer 6. As the dispersion contacts thecellulosic layer, absorption of the molten wax by the cellulosic layerbegins. The dispersion 4, the metallic layer 6 and the cellulosic layer5 pass between hot rolls 7 and 8. These hot rolls 7 and 8 cause theremaining wax to be rapidly absorbed by the cellulosic stock and thepolymer particles to melt while the pressure spreads the moltenparticles into essentially one continuous layer. Rolls 7 and 8 can be atthe same or different temperatures. Afterwards the article is cooled bycold rolls 9 and 10 causing the molten polymer to solidify.

FIG. 2 is a cross-sectional view of the finished article 11 prepared bythe aforementioned method. The outer layer 11c represents the cellulosicstock 5 ,now impregnated with wax from the wax polymer dispersion 4. Themiddle layer 11b is essentially a continuous polymeric layer, thepolymer being from the waxpolymer dispersion 4. Because substantiallyall the wax is absorbed by the cellulosic layer 11c and the polymer isinsoluble in the molten wax, the polymeric layer is substantially allpolymer. The polymeric layer is continuous in the sense that itcontributes to the total barrier property of the finished article eventhough pinholes might exist. These pinholes are extremely small holesand occur even, for example, when extruding a continuous thermoplasticpolymer film. The outer layer 11a represents the metallic layer 6 beingfirmly bound to the polymeric layer 11b, the polymer being from thewax-polymer dispersion 4. t

The aforementioned metallic layer can be a foil prepared from suchmetals as aluminum, steel, silver, ,gold, tin, lead or an alloy such astin-lead. The thickness of the foil can very widely; usually the rangethickness of the foil is determined by the desired properties of thelaminated article.

In practicing this invention, the cellulosic layer must be able toabsorb wax at a reasonable rate. Thus a cellulosic layer coated with orimpregnated with a substance which would substantially slow down the waximpregnation rate would be unsatisfactory. Typical wax absorption timesfor coated and uncoated cellulosic materials are shown in the followingTable I.

TABLE I Wax Absorption Time of Various Cellulosic Materials thicknessSurface Wax Absorption Material mils Coating Time, minutes Kraft linerboard 85 No l Corrugated board 10 1 Cup board 14 3.5 Chip board 33 0.5Oil can cardboard 26 0.5 Freezer carton Regular density l 3 Mediumdensity 10 0.5 Paper plate 20 l 5 20 1.5 Oil can cardboard 26 Yes 6 to10 28 Yes and 50 to 70 printed Freezer carton Regular density 10 Yes 35Medium density 18 20 to 22.5 Bread wrapper 12 Glassine paper 1.33 100"'Time required for a 0.1 ml. drop of wax to be absorbed into a testsheet at 160 F.

"These materials are deflned in THE DlCTlONARY OF PAPER, 3rd Edition,American Paper and Pulp Association. 1965.

The data in Table 1 indicates that Kraft liner board would be apreferred cellulosic material to be used with this invention whereas acoated material such as medium density freezer carton having a waxabsorption time of 20 to 22.5 minutes would be a less preferredcellulosic material.

The cellulosic layer, in addition to absorbing the wax at a reasonablerate, must be able to absorb substantially all the wax applied to itssurface. If sufficient wax remains unabsorbed, the strength of the bondbetween the metallic layer and the middle layer of wax and polymer isweak, depending on how much wax remains unabsorbed. Weak means that themetallic layer can be easily separated from the wax impregnatedcellulosic layer. Furthermore, a wax and polymer middle layer would havepermeation properties different from just a polymer middle layer. Thus aweak bond and a lack ofa middle polymer barrier are avoided by havingthe cellulosic layer absorb substantially all the wax.

The pulp used to make the various cellulosic layers that can be used inthis invention can be derived from a suitable source such as wood,reclaimed paper, cotton fibers and other fibers such as manila hemp,jute, etc.

The wax used herein can be a petroleum wax obtained by any one of theprocesses described in Chapter 5 of THE CHEMISTRY AND TECHNOLOGY OFWAXES by A. H. Warth, 2nd Edition and can be any one of the refined orunrefined petroleum waxes described in the same chapter. Synthetic waxesthat can be used are described in Chapter 6 of the aforementionedreference.

Petroleum wax is commercially available with a wide range of physicalproperties. Paraffin waxes are available with melting points from about126F. to 153F.

(ASTM D87), oil contents from about 0.1 to about 1.2 percent (ASTMD721), penetration at 77F. from about 9 to 40 (ASTM D1321), specificgravity at 212F. from about 0.756 to 0.767 (ASTM D287). Microcrystallinewaxes are available with melting points from about 151 to 193F. (ASTMD127), oil contents from about 0.4 to about 1.5 percent (ASTM D721 andspecific gravity at 212F. from about 0.786 to 0.795 ASTM D287). Whilethese different petroleum waxes will be absorbed at different rates byvarious cellulosic stocks, our invention can be used with any petroleumwax fraction that will be absorbed by the stock.

If a thermoplastic polymer which is soluble in molten wax at atemperature below the melting point of the polymer is used with thisinvention, the following problems arise. First if the polymer is solublein the molten wax at a temperature below the melting point of thepolymer, the viscosity of the resulting combination is drasticallyincreased. This resulting high viscosity combination is very difficultto handle and to apply a layer. Furthermore, on contacting thecellulosic layer, the combination is absorbed by the layer and,therefore, the wax-polymer impregnated cellulosic layer cannotcontribute the desired barrier properties of just a wax impregnatedcellulosic layer. The remaining combination, after having pressureapplied, forms a relatively weak polymer-wax bond between the metallicand cellulosic layers. Finally, the inner layer, being a wax-polymerblend, cannot contribute the desired barrier properties of just polymer.Thus to avoid the heretoforementioned problems, the thermoplasticpolymer used with this invention must be substantially insoluble in themolten wax at a temperature below the melting point of the polymer.

Another requirement of the thermoplastic polymer forming the middlelayer of the tri-layer laminated article is that it have an adhesivecapacity for both the metallic and cellulosic layers. Thus the middlethermoplastic polymeric layer, in addition to contributing to the finalbarrier performance of the article, acts as an adhesive holding themetallic layer to the wax impregnated cellulosic layer. Normally anadhesive in a laminated article, i.e., the material holding two layerstogether, does not contribute substantially'to the barrier properties ofthe laminated article. Barrier properties, as used herein, refers tosuch properties as resistance of the material to the transmission ofwater vapor, gas and grease. Standard tests exist for measuring thesepermeability properties. However, in this invention the middlethermoplastic polymeric layer acts as a barrier and an adhesive.

Surprisingly, not all thermoplastic polymers which are insoluble inmolten wax at a temperature below the polymers melting point have anadhesive capacity for both the metallic and cellulosic layers. Adhesivecapacity as used herein means that peel strength as determined by amodified TAPPlT806-SM46 test of the laminated article is greater thanzero.

Examples of thermoplastic polymers which are substantially insoluble inthe molten wax at a temperature below the melting point of the polymerand have an adhesive capacity for both metallic and cellulosic materialsare as follows: polyamide, polyvinyl chloride, cellulose acetatebutyrate, polymethylmethacrylate,

polyethylene with a molecular weight in excess of 1,000,000,polycarbonate and polystyrene. Polyamide, polyvinyl chloride, celluloseacetate butyrate and polymethylmethacrylate are the preferred polymersto be used with this invention.

The polyamide can be an aliphatic polyamide such as nylon-3, nylon-4,nylon-6, nylon-7, nylon-8, nylon-9, nylon-l0, nylon-l l,nylon-l2,nylon-6,6, nylon-6,10, as well as copolymers such as nylon 6,6-6,l0.Also, the polyamide can be an aliphatic-aromatic polyamide such asnylon-6, T, or an all-aromatic polyamide such as poly(meta-phenylenediamine isophthalamide). The methods of preparing thesepolyamides as well as their physical and chemical properties are definedin Kirk- Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 16, 2ndEdition, page 1, etc.

One example of a thermoplastic polymer which is insoluble in molten waxbut does not have the adhesive capacity for both metallic and cellulosiclayers is isotactic polypropylene with a molecular weight of 600,000.

The thermoplastic polymer used in this invention, when added to the wax,is in the form of finely divided particles. If the particles are toolarge, say passing through 3 mesh but remaining on mesh, the resultingdispersion is unstable in that the particles settle out rapidly causingproblems during the application of the dispersion to a layer. Allreferences to mesh herein refer to U. S. Sieve Series. Even if thissettling problem can be overcome, the resulting polymer coating on thelayer is of nonuniform thickness and is not continuous; that is,there'are some areas where there is no polymer coating. These areaswould be substantially greater than the pinholes mentioned herein. Thuswhile this invention is operable if all the polymer particles passthrough a 20 mesh, it is preferable that all particles pass through 100mesh and even more preferable that all particles pass through 200 mesh.Particle size distribution also influences dispersion stability anddispersion viscosity. At the same wax-polymer ratios a wide rangeparticle distribution, compared to a narrow range particle distribution,tends to have a greater viscosity and hence greater stability. Thelimits as to particle size. distribution range can be easily determinedby those skilled in the art.

The weight ratio of the polymer to the wax used in this inventiondepends on dispersion stability and dispersion viscosity which in turndepends on polymer particle size and particle size distribution.Satisfactory weight ratios are 5 to 45 parts by weight of finely dividedpolymer and 55 to 95 parts by weight of wax; the preferred weight ratiosare 10 to 40 parts by weight of finely divided polymer and 60 to 90parts by weight of wax.

The preliminary step in practicing this invention is to prepare thedispersion. Solid wax is placed in a suitable container and heated untilthe wax becomes molten; but the resulting temperature should not exceedthe melting point of the polymer being used. After the wax melts, thepolymer is added; mild agitation is usually necessary to form thedispersion. Alternatively, both the solid wax and the polymer particlescan be placed in a container and heated together to a temperature belowthe polymers melting point. Immediately after the dispersion has beenprepared it can be used or it can be cooled and the resulting solid usedat a later time. The permissible temperature range used to prepare thedispersion depends on the melting point of the specific wax being usedand the melting point of the specific polymer being used.

The dispersion, consisting of molten wax and polymer particles, isapplied to an outer layer in one of several ways. One method has alreadybeen discussed in connection with FIG. 1. Another method is that thedispersion is applied to the inner surface of a moving horizontalcellulosic layer. The application of a uniformly thick layer ofdispersion to the layer can be obtained by using a doctor blade, or byextruding (curtain coating), or by a roll coater or some other suitableequipment.

As soon as the dispersion touches the cellulosic material, the latterstarts to absorb the wax. The interval of time during which thisabsorption occurs before the metallic layer is placed adjacent to thedispersion depends on the equipment used, the wax absorption rate of thelayer and the amount of wax applied per surface area of cellulosiclayer. This interval of time can range from a fraction of a second tomany minutes. An example of the former is as follows. An extrudeddispersion film, containing a relatively small percentage of wax,contacts the cellulosic material and immediately thereafter the metalliclayer is placed adjacent to the dispersion film. Almost simultaneouslythe resulting composite comes into contact with heated rollers. Theseheated rollers raise the temperature of the dispersion to above thefusion point of the polymer and apply the desired pressure to the moltenpolymer particles. Thus substantially all the wax absorption by thecellulosic material occurs after the metallic layer is placed adjacentto the dispersion.

Alternatively, an example of where the time interval is relatively largeis as follows. The dispersion, containing a relatively large percentageof wax, is applied to the cellulosic material but the metallic layer isnot brought adjacent to the dispersion until substantially all the waxis absorbed by the cellulosic layer. During this long interveningperiod, the temperature of the dispersion must be above the meltingpoint of the wax but below the melting point of the polymer. A minoramount of wax can remain unabsorbed so that the polymer particles remainevenly distributed on the stock during movement of the cellulosic layer.

In the aforementioned examples, the dispersion is first applied to thecellulosic layer and then the metallic layer is brought adjacent to thedispersion. The converse is also operable without changing theproperties of the resulting article. That is to say, the dispersion canbe applied first to the metallic layer and subsequently the cellulosiclayer brought adjacent to the dispersion without affecting theproperties of the resulting article.

However, the former method is preferred.

heat to the metallic layer is preferred since it conducts heat morereadily than the cellulosic layer. The amount of pressure applieddepends on the type of polymer and ability of the layers, particularlythe cellulosic ones, to withstand the applied pressure withoutundesirable deformation. During this heat and pressure step, any

wax remaining unabsorbed is absorbed by the cellulosic material.

Another alternative method is as follows. After the dispersion isapplied to the cellulosic layer and sufficient time has elapsed so thatsubstantially all of the wax is absorbed, the polymer particles areraised to a temperature above their melting point by radiation and andthen the metallic layer is placed adjacent to the molten particles.After the metallic layer is in place pressure is applied. In thisalternative or any of the other alternatives defined herein, themetallic layer, prior to being placed adjacent to the dispersion, can beat a temperature greater than ambient temperature. However, the maximumtemperature of the metallic layer prior to being placed adjacent to thedispersion would be just below the decomposition temperature of thepolymer.

Subsequently, the composite can be allowed to cool or can be cooled bysuitable heat removal device. Cold roller are one example of the latter.

The following examples illustrate this invention:

EXAMPLES l-X To demonstrate that many thermoplastic polymers could beused, ten satisfactory runs were made as shown in Table ll. These runswere made in the following manner. Seventy-five parts of petroleum waxwere plain a suitable container and the temperature of the wax wasraised to above its melting point but below the melting point of thepolymer to be added. To the molten wax 25 parts of the polymer wereadded. Gentle agitation maintained the polymer particles uniformlydistributed in the wax. This dispersion was applied to a cup board stockin the following manner. An oven was maintained at 160F. In this ovenwas a roll of cellulosic material, i.e., cup board and several inchesaway was a doctor blade set to apply 2 to mils of dispersion. The cupboard moved from the mounted roll under the doctor blade and out of theoven. The molten wax-polymer dispersion was applied to the cup boardbetween the roll and the doctor blade. Thus as the cup board traveledunder the doctor blade a predetermined thickness of dispersion wasapplied. Note that the thickness must be limited to lay down no more waxcomponent that can be absorbed by the cup board. In these examples asthe cup board left the oven much of the wax was absorbed by the cupboard because of the slowness at which it moved.

Aluminum foil was placed on the coated surface of the cup board. Againstthis foil was placed a mirrorfinish plate (ferrotype) which was backedwith a second plate to facilitate handling. The resulting assembly wasplaced between the platens of a press. The platen to be brought intoimmediate contact with the back side of the polished plate was preheatedto a temperature sufficient to fuse the specific polymer. The platenswere closed loosely for a few seconds to heat thepolished plate and thepolymer particles. The pressure was then raisedto about 500 p.s.i. andmaintained for a short time (about 10 sec.). The pressure was released,and the assembly was removed from the press and cooled'to about roomtemperature. The resulting product was a tri-layer laminated articlehaving an outer aluminum foil layer, an essentially continuous middlepolymer layer of a thickness of about 0.001 inch and an outer waximpregnated cup board. The aluminum foil adhered firmly to the polymeras indicated by the peel strength data shown in Table Il.

TABLE [I Polymers and Temperatures Used To Prepare Laminated Articles:Aluminum F oil-Polymer-Wax Impregnated Cup Board Melting I point ofFusion Peel Strength (0 Run Polymer polymer-F Temp.F.lbs/3" Width 1nylon-ll 376 410 3.45 2 nylon-6,6 500 520 1.38 3 nylon-6,10 410 430 1.064 nylon-l2 347356 430 0.30 5 nylon-6 425 430 0.18 a polyvinyl- 300 3250.50

chloride 7 cellulose acetate (e) 265 330 0.30

butyrate" 8 polymethylmeth 390 400 0.20

acrylate 9 polyethylene" 285 310 0.1 10 polystyrene 250 310 0.1

(a) Molecular weight of (b) Medium impact (c) One mill thickness (d)Properties of cup board: l4 mils, 62 lbs. per 1000 sq. ft.

(e) Contains l3 wt.% acetyl groups & 37 wt.& butyl groups (f) ModifiedTAPPl-T806-SM 46, dry test on 3 inch wide specimen at rate of 2inch/min. and foil being pulled at l.

Use of either the bright smooth side or the dull rough side of thealuminum foil to contact the dispersion gave equivalent results.

For comparative purposes a tri-layer article of aluminum foil-wax-waximpregnated cup stock was prepared in an analogous manner. The peelstrength of this tri-layer article was zero. Also, for comparativepurposes a tri-layer laminated article of aluminum foilnylon-1 l-porouscup stock was prepared in an analogous manner. The peel strength of thisarticle was a tear seal, i.e., rather than the foil separating throughthe polymeric layer from the cup stock the cup stock itself was torn.However, this latter article does not have any of the desired waxbarrier properties.

A unsuccessful tri-layer article of aluminum foilisotactic polypropylenewith a molecular weight of about 600,000 wax impregnated cup stock wasprepared in a similar fashion to that described for runs 1 to 10. Thearticle was unsuccessful in that the peel strength was zero.

EXAMPLE XI Using steel foil in place of aluminum foil, a laminatedarticle of steel foil-nylon-l l-wax impregnated cup board was made in asimilar fashion to that described for Examples l-X. This laminatedarticle had a tear seal.

The petroleum wax used in Examples l to Xl had the followinginspections:

Melting point, ASTM D87 126F. Oil Content, ASTM D721 0.4 Color, Saybolt,ASTM Dl56 +29 Penetration at 77F, ASTM Dl32l l8 Viscosity, SUS at 210F.,ASTM D446 38.8 Specific gravity at 212F., ASTM D287 0.760

a. establishing a heterogeneous composite of thermoplastic polymer infinely divided form and molten wax, said polymer having an adhesivecapacity for both metallic and cellulosic materials and a melting pointabove the melting point of the wax and being substantially insoluble inmolten wax at a temperature below the melting point of the polymer;

b. applying a coating of said heterogeneous composite to an innersurface of an outer cellulosic layer at a temperature above the meltingpoint of the wax but below the melting point of the polymer, the amountof coating being regulated so that substantially all of the wax thereinis absorbable in the cellulosic layer and allowing sufficient time topermit the wax to start to absorb into said cellulosic layer and then;

c. placing the other outer metallic layer adjacent said coating;

d. heating the coating to a temperature above the melting point of thepolymer and pressing the outer layers against the coating to form anessentially continuous molten polymer layer between the metallic layerand cellulosic layer whereby absorption of molten wax into the porouscellulosic layer occurs;

e. and thereafter cooling the molten polymer whereby it solidifiesresulting in said article.

2. A method according to claim 1 wherein said heterogeneous compositecontains 5 to 45 parts by weight of finely divided polymer and 55 toparts by weight of said wax.

3. A method according to claim 2 wherein all the finely divided polymeris finer than mesh (U.S. Sieve Series).

4. A method according to claim 3 wherein the polymer is selected fromthe following group: polyamide, polyvinylchloride, cellulose acetatebutyrate, polymethylmethacrylate, polyethylene with a molecular weightin excess of 1,000,000, polycarbonate and polystyrene.

5. A method according to claim 4 wherein the metallic layer is selectedfrom the following group: aluminum, steel, tin, lead, silver, gold andtin-lead alloy.

6. A method according to claim 5 wherein the polymer is selected fromthe following group polyamide, polyvinylchloride, cellulose acetatebutyrate and polymethylmethacrylate.

7. A method according to claim 1 wherein the wax is a petroleum wax.

8. A method according to claim 7 wherein the polymer is selected fromthe following group: polyamide, polyvinylchloride, cellulose acetatebutyrate and pogymethylmethacrylate,

. A method according to claim 8 wherein said heterogeneous compositecontains 10 to 40 parts by weight of finely divided polymer and 60 to 90parts by weight of said wax, all the finely divided polymer is finerthan 100 mesh (U.S. Sieve Series), said polymer is selected from thefollowing group: nylon-l l nylon-6,6 nylon-6,10 and said metallic layeris selected from the following group: aluminum and steel.

1. Method of preparing a tri-layer laminated article, having an outerwax-impregnated cellulosic layer, a middle thermoplastic polymeric layerand an outer metallic layer, comprising: a. establishing a heterogeneouscomposite of thermoplastic polymer in finely divided form and moltenwax, said polymer having an adhesive capacity for both metallic andcellulosic materials and a melting point above the melting point of thewax and being substantially insoluble in molten wax at a temperaturebelow the melting point of the polymer; b. applying a coating of saidheterogeneous composite to an inner surface of an outer cellulosic layerat a temperature above the melting point of the wax but below themelting point of the polymer, the amount of coating being regulated sothat substantially all of the wax therein is absorbable in thecellulosic layer and allowing sufficient time to permit the wax to startto absorb into said cellulosic layer and then; c. placing the otherouter metallic layer adjacent said coating; d. heating the coating to atemperature above the melting point of the polymer and pressing theouter layers against the coating to form an essentially continuousmolten polymer layer between the metallic layer and cellulosic layerwhereby absorption of molten wax into the porous cellulosic layeroccurs; e. and thereafter cooling the molten polymer whereby itsolidifies resulting in said article.
 2. A method according to claim 1wherein said heterogeneous composite contains 5 to 45 parts by weight offinely divided polymer and 55 to 95 parts by weight of said wax.
 3. Amethod according to claim 2 wherein all the finely divided polymer isfiner than 100 mesh (U.S. Sieve Series).
 4. A method according to claim3 wherein the polymer is selected from the follOwing group: polyamide,polyvinylchloride, cellulose acetate butyrate, polymethylmethacrylate,polyethylene with a molecular weight in excess of 1,000,000,polycarbonate and polystyrene.
 5. A method according to claim 4 whereinthe metallic layer is selected from the following group: aluminum,steel, tin, lead, silver, gold and tin-lead alloy.
 6. A method accordingto claim 5 wherein the polymer is selected from the following grouppolyamide, polyvinylchloride, cellulose acetate butyrate andpolymethylmethacrylate.
 7. A method according to claim 1 wherein the waxis a petroleum wax.
 8. A method according to claim 7 wherein the polymeris selected from the following group: polyamide, polyvinylchloride,cellulose acetate butyrate and polymethylmethacrylate.